The present invention relates to a magnetic gear and a centrifuge having a magnetic gear, in particular a flow-through centrifuge without axial face seals used for centrifuging biological fluids such as blood.
In a conventional flow-through centrifuge, blood which is to be separated into its different components flows through an inlet line into a rotating centrifuge chamber, and the separated components are removed from the centrifuge chamber through outlet lines. Management of the inlet and outlet lines can be difficult, because of the relative movement of the centrifuge chamber and the stationary connection of the lines. Traditional flow-through centrifuges use rotating joints to prevent the lines from twisting.
German Patent Application DE-A 32 43 541 describes a centrifuge without axial face seals, where the inlet and outlet lines are carried in a loop around the centrifuge chamber at half the Revolutions Per Minute (rpm) of the centrifuge chamber. To do so, the lines are connected to a rotating frame which rotates at half the rpm of the centrifuge chamber. The rotating frame is connected to a hollow shaft, the drive for the centrifuge chamber being provided with a drive shaft extending through the hollow shaft. A belt drive is used to transfer the torque to the hollow shaft and the drive shaft.
International Patent WO 96/40322 describes a centrifuge characterized by a very compact design. The centrifuge chamber and the line-entraining mechanism are driven at half the rpm and in the same direction of rotation as the chamber by means of a toothed gear. However, the relatively high operating noise of the gear wheels is a disadvantage of this design. Furthermore, the use of gear wheels requires high precision manufacturing of the centrifuge, which is thus complicated and expensive. In addition, the gears must be lubricated, which not only increases maintenance but also leads to a collection of dirt and soiling. Moreover, the gears are subject to constant wear.
Magnetic gears are known for transmission of torque. European Patent EP 849,869 A2 describes a gear having several parts that move relative to one another and work together magnetically, one part being provided for a connection to a drive shaft and one as a stationary part. The individual parts are designed as ring-shaped bodies arranged concentrically.
The present invention is a very compact magnetic apparatus for a centrifuge, in particular for a flow-through centrifuge without axial face seals, which permits largely maintenance-free operation of the centrifuge at a high rpm with low noise and with relatively low driving power.
In one embodiment, the invention is a magnetic gear magnetically connecting a plurality of carriers rotatable relatively to one another. The invention includes a first and a second carrier, a plurality of magnetic poles disposed in a circle on each of the first and second carrier, with a gap separating adjacent magnetic poles, the plurality of magnetic poles being arranged in an alternating positive pole and negative pole configuration, and a third carrier. The third carrier has at least two pairs of flux-carrying connecting pieces, wherein said flux-carrying connecting pieces are arranged so that, in a first rotational position of the carriers, a first section of the first pair of flux-carrying connecting pieces faces the gap between two adjacent magnetic poles of the first carrier, and a second section of the first pair of flux-carrying connecting pieces faces the gap between two adjacent magnetic poles of the second carrier. Additionally, in the first rotational position of the carriers, a first section of the second pair of flux-carrying connecting pieces faces a magnetic pole of the first carrier, and a second section of the second pair of flux-carrying connecting pieces faces a magnetic pole of the second carrier.
The magnetic gear has a first and second carrier, each having a plurality of magnetic poles arranged on a circle with spacing gap between them, and with the north and south poles alternating. The magnetic coupling of the first and second carriers is accomplished by a third carrier which includes the flux-carrying connecting pieces.
To transmit a torque from a drive shaft to a driven shaft, one of the carriers is stationary while the other two carriers are connected to the drive shaft and the driven shaft. When one of the two rotating carriers is driven at a certain rpm, the other rotating carrier rotates at a certain rpm in the same direction or in the opposite direction, with the direction of rotation and the rpm depending on the configuration of the magnetic poles and the connecting pieces.
To magnetically couple the first and second carrier, the third carrier has at least two pairs of flux-carrying connecting pieces. These pieces are arranged so that, in a starting position, a first section of the first pair of flux-carrying connecting pieces is facing a gap between two adjacent magnetic poles of the first carrier, and a second section of the first pair is facing a gap between two adjacent magnetic poles of the second carrier.
At the same time, a first section of the second pair of flux-carrying connecting pieces is facing a pole of a magnet of the first carrier, and a second section of the second pair is facing a pole of a magnet of the second carrier. If the carriers are rotated relative to one another, the starting condition as described above is again established, where the one pair of flux-carrying connecting pieces is facing a gap and the other pair is facing a magnetic pole. In these starting positions, the magnets generate a magnetic flux which is closed over the flux-carrying connecting pieces.
In one embodiment, the first and second carriers can be parallel disks on whose facing sides magnets are arranged. However, the magnets can also be arranged on the periphery of the disks. The configuration can be changed as long as the magnetic poles are arranged on a circle at a distance from one another, with the north and south poles alternating and the magnetic flux being closed over the connecting pieces. The first and second carriers preferably have the same diameter, so that the magnets are directly opposite one another. However, the carriers may also have different diameters and/or a different number of magnetic poles, so that one row of magnets is offset relative to the other row of magnets.
In another embodiment, the magnetic poles can be arranged at uniform distances on the first and second carriers, with the distance between the magnetic poles preferably being equal to the width of the magnets. The width of the flux-carrying connecting pieces preferably corresponds to the distance between the magnets. The geared drive and the driven carriers are then engaged especially rigidly, and torque can be transmitted smoothly.
To close the magnetic flux over the first and second carriers, the two carriers can each be preferably made of a soft magnetic material. However, the carriers need not be made completely of soft magnetic material. Only the parts of the carrier between the magnets can be made of a soft magnetic material, and still be sufficient to close the magnetic flux.
The flux-carrying connecting pieces may consist of either one or two flux-carrying elements arranged with a distance between them. When two flux-carrying elements are provided for each connecting piece, it is possible to prevent the magnetic flux generated by the magnets of a carrier from being closed directly over the connecting piece. To reduce eddy current losses, the connecting elements of the connecting piece may in turn be made of a plurality of sheets of magnetic sheet steel insulated from one another.
The flux-carrying connecting pieces may be shaped in various ways. An important parameter is that the first and second sections of the flux-carrying connecting pieces must extend between the opposite magnets of the two carriers, forming a narrow air gap. The first and second sections of the flux-carrying connecting pieces can preferably have their end sections arranged close to the magnets. However, the connecting pieces may also extend beyond the magnets on both sides.
When applying the magnetic coupling according to the invention to a centrifuge for separating fluids, in one exemplary embodiment the first carrier can be arranged in a stationary mount on a frame. The third carrier can be a rotating element arranged rotatably on a frame, while the second carrier can be a separation unit arranged on the rotating frame. For rotating the separation unit, the rotating frame is driven. To do so, the rotating frame may be connected to a drive shaft extending, for example, through the stationary carrier. However, other types of drives are also possible.
A centrifuge utilizing a magnetic drive gear is characterized by a very compact design. It can be operated largely maintenance-free at a high rpm with a relatively low driving power and a low noise level.
The magnetic gear can be designed so that the separation unit rotates at twice the rpm of the rotating frame. This can be accomplished using two parallel disks, preferably having the same diameter as the carriers, on which the same number of magnetic poles are arranged at equal intervals. Although the ratio of the magnetic poles on the carriers reflects the ratio of rpm""s. the position of the flux-carrying connecting pieces determines the direction of rotation.
The line for supplying and for removing at least one fluid can preferably be carried from a stationary connection around the separation unit, and can be connected to the separation unit on a side of the line facing away from the stationary connection point. Twisting of the separation unit is prevented if the separation unit rotates at twice the rpm of the rotating frame.
Other objects, features and advantages of the invention will be readily apparent from the following detailed description of a preferred embodiment thereof taken in conjunction with the drawings.